This is FRESH AIR. I'm Terry Gross. The Koch brothers, Charles and David, are famous for the wealth they've amassed through Koch Industries - together they're worth more than $100 billion - and for creating a powerful political influence network. The network is designed to amplify messages pushed by Koch Industries, support legislation that favors Koch's needs and goals and defeat legislation that stands in the way of Koch profits. Koch has used this network to prevent or try to dismantle regulations that affect the businesses.

David Koch, one half of the billionaire duo that built one of the nation's largest privately owned companies and one of its most controversial political networks, has announced his retirement from politics and business.

In a letter to Koch Industries employees written by his brother Charles Koch, the men announced that David was stepping down due to health concerns.

For years the political network funded by billionaires Charles and David Koch funded politicians on the right, laying the foundation for the libertarian causes the two support. Their support has gone almost exclusively to Republican candidates, with rare exception.

But in the era of Trump, what it means to be on the "right" is changing, and the Koch network's tactics are changing to reflect new realities.

The head of the Environmental Protection Agency, Scott Pruitt, has proposed a new rule that restricts scientific research that can be used by the agency for its regulatory decisions.

The proposed rule only allows the use of studies that make all data publicly available for anyone to analyze. Pruitt proposed the new rule as a way to make the agency's decision-making more "transparent, objective and measurable."

A conservative group funded by billionaire brothers Charles and David Koch is turning its attention to a new front: promoting federal judges at the grass-roots level. Americans for Prosperity is willing to spend nearly $1 million to confirm judges this year. Those lifetime appointments could reshape the courts for a generation.

"The fact of the matter is that so much of what affects us in our daily lives plays out in the courtroom," said Sarah Field, the group's new vice president for judicial strategy.